For a current transformer you need to know the number of turns, and this can be roughly measured (its likely to be a nice round number fortunately).
Measurement means you need a known source of AC current at mains frequency. You also need to place a multimeter in AC current measuring mode across the output of the clamp sensor. Don't try to measure its voltage, you must short-circuit the output with a current meter. The ratio of current through the clamp jaws to the measured current from the sensor is the number of turns. Expect a value of several hundred or thousand turns (ie 10A rms through the jaws you'd expect something in the range around 10mA at the output).
Or try asking at the current-cost blog...